For paul fronczak a mission has become an obsession. Between breakfast and ballet lessons he's on the hunt. I work a full time job, i have a family, but this, this is my life. And this is my only shot at solving these mysteries. So, I put as much time as i, as I can. Everyone goes to bed at night, I'm, I'm on line, researching. Reporter: His focus is finding his parents' stolen baby. But he is still searching for clues to his own identity. I feel kind of like an imposter because I am still using his birth certificate. Paul is out there, and I have his birth certificate and I want to give it to him. And I want to find mine. Reporter: Desperate to find any connection to his biological family, paul sent dna samples to the genealogy site ancestry.Com. We took the sample that you gave us and we put it on a chip. And what that does is, it gives us a unique dna signature that only you have. So we compare your dna to dna from populations all over the world. So, you're kind of like csi but you work with dna. It's family history. Reporter: The results were paul's first indication of who he is and where he's from. There were surprises about his ethnic roots. You are, 37%, according to our analyses, of european-jewish descent. Wow. Is that new? Well, I was raised a roman catholic. Well -- so this is interesting. I was baptized twice, actually. And I'm actually jewish. So, it's kind of cool. I have to learn a whole new religion now. I'm excited about that. Reporter: Even more exciting, a major development in ancestry.Com's search. Finally, a link to his first blood relative, a third cousin. I saw third and I'm like oh! This is close, this is good, right? It was like a lottery when I saw that. If you communicate with her and she wishes to work with you and help with you looking at a family tree, it could actually be very informative. Reporter: You have been in touch with that cousin. I have. She got back to me and said, "wow, how can I help?" Reporter: And how has she helped? She sent me a list of her relatives. I believe that once we actually have that family tree we can start looking for where my dna overlaps with their family. Reporter: If any of her relatives lived in or near new jersey, where paul was abandoned, they could be the key to unlocking the mystery of who he is. We have to kind of work on that path. Reporter: To see if anybody really does know who you are or what happened? Right. Reporter: How much a part of your life is this whole search. Right now it is a lot. It's like he's on a mission and he doesn't want to stop until he finds answers. Reporter: Does that bother you? Yes. I think he needs to put the brakes on a little bit. Like he's kind of missing out on just everyday things. It's always there for him. It's something you can't do at a 9:00 to 5:00 job. It's not like punching in, "i'll find out who I am today. Oh, gotta punch out for lunch." You can't do that. Reporter: Being a detective of his own life has taken at toll on paul and on his wife michelle. There are many days where i know he wants to cry, and I want to cry, too, but you know, you can't. Are you crying? I get sad when I think about it. Like when we really talk seriously about it, it makes me sad. Reporter: As for paul's parents michelle says there is now a rift that she hopes can soon be repaired. They love him. They don't care whether he's their biological son. Paul is their son. I think what they're feeling right now is that maybe they weren't -- maybe they're questioning, "why do you wanna do this? We're your parents. Are -- were -- aren't we good enough?" And I think that they're maybe feeling as though he wasn't happy with his upbringing. But that's not the truth. Yeah, and I just -- I can't understand that -- that kind of thinking. If anything, it should get stronger by finding out these missing links. I mean, how could you not want to know what happened to your kidnapped child? Reporter: So the search continues and the hope that a tragic mystery can one day end in a reunion 50 years in the making. Reporter: If you found the real paul fronczak, what would you say? First I think I'd have to give him a really long hug, and say I've been looking for you for a long time, pal. And then I'd just ask him how he is, how was his life. Reporter: You know, you may never find the answers. But I might. And he might, after tonight's broadcast. would help with the investigation, then contact us at abc news.Com/20/20, you can

This transcript has been automatically generated and may not be 100% accurate.

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{"id":20763039,"title":"A Mission Becomes an Obsession","duration":"4:56","description":"Act 6: There's a major development in Fronczak's search for his true identity and biological family.","url":"/2020/video/mission-obsession-20763039","section":"2020","mediaType":"default"}